One other issue that should be noted with the URL for the share buttons that I encountered.
I noticed that when the page for the link resolves in the dialog box; if you have a testing server defined, the url will use that definition rather than what might be the actual URL.
For example, I might have a site that online is "example.com". But my testing server is just set up and defined in DW as "http://example/". I do this on my box that way, so on my testing server, there is no dot com (or whatever extension) and then I just type in ".com" to see the live production version.
But in the dialog box, it will just pull it as "http://example/page.php" rather than "http://example.com/page.php".
Now, while I think people should be smart enough to change that, I also know the reality that there are people that will say it doesn't work because they want to extension to "think" for them too.
So my suggestion would be to use the PHP Server Name variable to automatically pull the server root and then just allow for selecting the page in the dialog with the correct parameters.
So the extension would write this before the page:
<?php $_SERVER['SERVER_NAME']; ?>/page.php